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Discovery of an Unusual High State in the Long-Term Light Curve of AM Herculis

Kafka, S. and Hoard, D. W. (2009) Discovery of an Unusual High State in the Long-Term Light Curve of AM Herculis. Publications of the Astronomical Society of the Pacific, 121 (886). pp. 1352-1358. ISSN 0004-6280.

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The magnetic cataclysmic variable archetype AM Herculis is known to display high and low photometric states, in which it switches from Roche lobe-overflow accretion (high) to wind accretion (low). The origin of this behavior is still unknown (although it is believed to be linked to the presence of starspots located near the L1 point on the secondary star), as are the specifics of duration and frequency of the two states. During the recent (2007) transition from an exceptionally long period of persistent low state behavior back to the high state, AM Her entered a short (~2 month) intermediate state, in which its brightness remained at ~0.5 mag fainter than the normal high-state level. Within the recorded history of AM Her, this was the first time the system displayed such behavior. Using data from the American Association of Variable Star Observers, we compare the characteristics of this faint high state to the subsequent normal high state, and a prior "failed high state," in which the system briefly reached a brightness level near that of the normal high state before rapidly returning to the low state. The distribution of magnitude values attained during each state, along with the shapes of the orbital light curve in each state, support a scenario in which the specific configuration of the accretion flow between the secondary star and the white dwarf must be rapidly established at the end of a low state, even before the mass transfer rate has reached the normal high-state level.

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Hoard, D. W.0000-0002-6800-6519
Additional Information:© 2010 University of Chicago Press. Received 2009 September 6; accepted 2009 September 29; published 2009 November 12. We would like to thank Kent Honeycutt for making the RoboScope data available to us, and for constructive discussions. We acknowledge with thanks the variable star observations from the AAVSO International Database used in this research that were contributed by the following observers: Keith A. Graham, Stephen E. Robinson, Robert A. James, Francois M. Teyssier, Bill Goff, Ronald E. Zissell, Walter MacDonald, Tomas L. Gomez, Donn Starkey, John Blackwell, Zsolt Kereszty, Timothy R. Crawford, Ronald E. Royer, Don Wells, Kevin Kessler, Tom Michalik, Martin Nicholson, Danny Scharnhorst, Roger Diethelm, Mauro Graziani, Andrzej Arminski, Richard P. Harvan, Gary Walker, Shawn Dvorak, Massimo Banfi, Thomas McDonagh, Dennis G. Hohman, Marino Fonovich, Michael Koppelman, John Grainger Observatory, Lewis Cook, Frank L. Scheder, Richard Sabo, Frans D.J. Nieuwenhout, Michael Simonsen, Jerry Doug West, Alain Bruno, Herve Chantegros, William Alexander, Aengus O’Fearghail, David A. Hurdis, Timothy Hager, William J. Aquino, Richard Huziak, Pere Closas, Marco Fiaschi, Alexandru Corlan, Barbara Harris, Ronald Baker, Richard Campbell, Kevin Krisciunas, Steve O’Connor, James Willams, William Dillon, David Scott Reynolds, Radu Corlan, Charles A. Suslavage, James A. Case, Horace Smith.
Issue or Number:886
Record Number:CaltechAUTHORS:20100108-090600054
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Official Citation:Discovery of an Unusual High State in the Long-Term Light Curve of AM Herculis S. Kafka and D. W. Hoard Publications of the Astronomical Society of the Pacific 2009 121:886, 1352-1358
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:17103
Deposited By: Joy Painter
Deposited On:11 Jan 2010 23:35
Last Modified:17 Nov 2019 05:06

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